The present invention relates to a display device and a display method and, more particularly, to a display device and a display method using a non-light emitting element.
As a display device having pixels arrayed in a matrix manner, a liquid crystal display (to be referred to as an LCD hereinafter) is widely used. An LCD has the advantages that a small and thin display can be formed and a large screen can be realized by improving an optical system. Therefore, research and development of LCDs are being extensively made.
An LCD displays images by using changes in the optical characteristics of a liquid crystal material due to voltage application. A typical LCD has a structure in which a liquid crystal layer is sandwiched between a pair of substrates which have electrodes on their opposing surfaces and are subjected to an alignment treatment, and polarizing plates are adhered to the outer surfaces of these substrates.
In this LCD, only a light component in a specific polarizing direction of light emitted from a light source is sent into the liquid crystal layer, and the polarizing direction of light emerging from the liquid crystal layer is changed in accordance with the voltage applied to the liquid crystal layer, thereby changing the quantity of transmitted light. Hence, the light utilization efficiency of this LCD is a maximum of at most 50%, and less than 10% in reality. Therefore, an LCD like this requires a high-luminance light source, and this increases the ratio of the consumption power of the light source to the whole consumption power. Additionally, in an LCD the influence of light leaking when dark colors are displayed is large, so it is difficult to realize high contrast.
As a technique for solving the above consumption power problem, U.S. Pat. No. 4,822,145 has disclosed an LCD using a combination of a light source and a plate-like light waveguide. This LCD has a structure in which a liquid crystal layer is formed in contact with one surface of the waveguide. In this display device, when dark colors are displayed, light from a light source is confined in the waveguide by total reflection. When light colors are displayed, the light confined in the waveguide is fed into the liquid crystal layer by changing the alignment state of liquid crystal molecules and is thereby output to the outside as display light. This display device can reduce the consumption power of the light source. However, this display device cannot realize high contrast because a liquid crystal is used to switch ON and OFF of pixels. Also, since the display device uses the waveguide, light entering the liquid crystal layer has no directivity. That is, output light from this display device is diffused light having no directivity. This makes it difficult to use this display device as a projection display in which a scattering surface is set apart from a liquid crystal panel.
Jpn. Pat. Appln. KOKAI Publication No. 11-73142 has disclosed a display device which, instead of using a liquid crystal, extracts light by moving a transparent member into contact with and away from one surface of a plate-like waveguide by using an actuator. In this display device, when dark colors are displayed the transparent member is moved away from one surface of the waveguide, thereby confining light from a light source in the waveguide by using total reflection. When light colors are displayed, the transparent member is brought into contact with one surface of the waveguide. Consequently, the light confined in the waveguide is output to the outside as display light from the side of the waveguide away from the transparent member. Since this display device uses no liquid crystal, high contrast can be realized. However, the output light is diffused light having no directivity because this display device also uses the waveguide. This makes this display device difficult to use as a projection display.